The present invention relates to optical fibers, and more particularly to the attachment of optical components to a substrate and to the alignment of the optical component to a laser.
There is a significant and growing demand in the optoelectronics industry for low cost fiber-coupled laser modules that are highly reliable. Fiber-coupled laser modules include an optical fiber that is aligned with a laser on a substrate and that is attached to the substrate. Single mode fiber devices require fiber-coupled laser modules. For example, fiber-coupled laser modules are used in pumps for fiber amplifiers, wavelength division multiplex (WDM) sources, high-speed and high-power distributed feedback (DFB) lasers, and semiconductor optical amplifiers.
Generally, the laser and the optical fiber are fabricated or mounted on a substrate. To achieve acceptable performance, the optical fiber must be precisely aligned to the laser. After alignment, the optical fiber must be securely attached to the substrate without adversely impacting alignment, damaging the laser or the optical fiber, or turning the laser off. Proper alignment ensures that the optical interface has a very high single mode coupling efficiency. The connection between the optical fiber and the substrate must also be capable of withstanding environmental conditions such as operating temperature variations, vibration, dust, etc. Other important attributes include a relatively high thermal conductivity between the laser and the substrate to allow high power operation of the laser.
The high thermal conductivity between the laser and the substrate may cause problems when connecting the optical fiber to the substrate using attachment methods that employ heat. For example, soldering is often used to attach the optical fiber to the substrate. Soldering involves heating the metallic parts that are to be connected together and using solder to bind the parts together. Oftentimes, an integrated resistor that is in a heat exchange relationship with the solder is used as a heat source for melting the solder.
Referring now to FIG. 1, a fiber-coupled laser module 10 according to the prior art includes a laser 12 and an optical fiber 14 that are attached to a substrate 16. Heat (identified by arrows 18) is generated during attachment of the optical fiber 14 to the substrate 16 using solder 20. Most of the heat 18 from the soldering operation tends to flow downward through the substrate 16 to a heatsink (not shown) such as a thermoelectric cooler (TEC). Due to the relatively high thermal conductivity of the path between the laser 12 and the substrate 16, some of the heat 18xe2x80x2 is also conducted to the laser 12. The heat 18xe2x80x2 may damage the diode or melt the solder that connects the laser 12 to the substrate 16, which decreases the reliability of the laser 12 and increases degradation of the solder connection. The heat 18xe2x80x2 can also cause misalignment of the laser 12 and/or turn off the laser 12 during alignment.
An optical connection module according to the invention attaches an optical component to a substrate and aligns the optical component to a laser. The optical connection module includes a fiber submount that is attached to the substrate and a thermally insulating material having a thickness greater than 20 micrometers. An optical component is soldered to the fiber submount by application of heat from a laser. A laser submount is attached to the substrate. A laser is attached to the laser submount.
In other features of the invention, the optical component is selected from active and passive optical components such as optical fiber, lenses, mirrors, filters, detectors, isolators, and microelectromechanical devices.
In still other features of the invention, a fiber bonding pad is located between the solder and the thermally insulating material. The fiber bonding pad has a lateral heat flow characteristic that is significantly greater than its vertical heat flow characteristic. The fiber bonding pad is located between the thermally insulating material and the optical fiber. The fiber bonding pad and the thermally insulating material conduct heat locally and laterally during laser soldering to uniformly melt the solder. The thermally insulating material and the fiber bonding pad limit heat transfer to the substrate during soldering. The fiber bonding pad also provides a robust attachment location for connecting the optical component. The thickness of the fiber bonding pad also helps conduct heat laterally. The fiber bonding pad also provides a solder dam.
In yet other features of the invention, the fiber bonding pad includes multiple layers. One layer is made of Au and another layer is selected from the group of Ni, Cr, Ti and CrO. Additional layers can be made of Ti and Pt.
In another feature of the invention, an integrated fiber-coupled laser module for aligning and attaching an optical fiber to a substrate includes a thermally insulating material formed integrally in the substrate and having a thickness greater than 20 micrometers. A fiber bonding pad includes at least one metallic layer attached to the thermally insulating material. An optical fiber is laser soldered to the fiber bonding pad. A laser is located on the substrate.
In still other features of the invention, the integrated thermally insulating material is formed by flame hydrolysis or by anodic bonding.
Further areas of applicability of the present invention will become apparent from the detailed description provided hereinafter. It should be understood that the detailed description and specific examples, while indicating the preferred embodiment of the invention, are intended for purposes of illustration only and are not intended to limit the scope of the invention.